Training military troops in the use of firearms can be made safer and less costly by utilizing blank ammunition. It is also beneficial to train troops with the same weapons they will be using in the field. This familiarizes the troops with weapon functioning, cleansing, maintenance procedures, etc. Usually, however, the bullet traveling through the barrel plays a vital role in the functioning of most military weapons. For example, it causes a back pressure that is utilized in recycling the moving parts of the weapon. Since there is no bullet when using blank ammunition, a blank firing attachment (BFA) must be used to create the pressures necessary to make the weapon operate normally.
The BFA normally consists of a bore restricting device placed on the muzzle of the weapon. The BFA limits the escape of gases generated by the firing of blank rounds. The restricted flow simulates the effect of a bullet in the bore. The weapon will then cycle automatically in the same manner as when it is using live ammunition.
In a recoil operated weapon such as the M2 machine gun, there is no gas system to cycle it. Instead, the gun depends on reaction forces (or kick) of the cartridge detonation to energize the recoiling parts. The barrel recoil initiates movement of the cycling parts. Without a BFA of some sort, a blank cartridge, when fired, does not have enough reaction force to recoil the barrel and hence recycle the moving parts.
There is an ever present risk of feeding a live round into the weapon. This presents an extremely dangerous condition when using the previously described BFA's. A live round fired through these BFA's can send shrapnel in all directions. This becomes a potential danger to the operator and any other personnel in the area. This is especially true in the case of the larger caliber weapons such as the .50 cal. M2 machine gun.